Colored gold alloy



Patented May 20, 1941 COLORED GOLD ALLOY Ludwig Weiss, Frankfort-on-the Main, Germany, assignor to Chemical Marketing Company Inc., New York, N. Y., a corporation of New York No Drawing. Original application May 1, 1940,

Serial No. 332,841. Divided and this application May 22, 1940, Serial No. 336,653. In Germany April 13, 19,39 4 Claims.

My invention relates to the manufacture of a purple colored gold alloy containing thorium besides aluminum and gold. This application is a division of my application S. N. 332,841, filed May 1, 1940.

'It is known that gold combines with aluminum and forms an intermetallic composition of the formula AuAlz with a blueish or purple, amethystlike color, containing 78.5 parts of gold and 21.5 parts of Al. This alloy, known as amethyst or blue gold is not workable because of its hardness, brittleness and its liability of breaking.

Other gold alloys contain, besides gold and aluminum according to the formula AuAlz, additional quantities of aluminum or other soft metals such as silver, tin, zinc, cadmium, bismuth, thallium either alone or-in combination in quantities which facilitate the workability of the alloy without a harmful influence to the color effect. The total amount of these additional soft metals should not excee f40% of the alloy. With these additions of soft metals gold alloys of various shades are obtained, for instance, from red over a purple shade to a violet color, i. e. especially amethyst colored red alloys which are workable and suitable for the manufacture of jewels.

Now is was found that the qualities of the goldaluminum alloys, especially those of the formula AuAl: may be considerably improved with respect to the workability by adding thorium in suitable amounts.

These new alloys according to my invention may, for instance, also contain thorium in quantities up to about 10%, besides gold and aluminum. If a beautiful blue color is desired, the contents of thorium in the alloy must be kept below 7%. It is also possible to 'add very small amounts of thorium, for instance, such which do not exceed 1% of the whole alloy. Gold aluminium alloys with a thorium content of, for instance, 0.5% to 1% have a beautiful shade, good workabality and ductility. The thorium content may even be kept lower, especially if other metals with improving qualities are present. The lower limit of the content of thorium is, for instance, about 0.5% of the total alloy.

Furthermore, I have found that the ductility of the alloys may be increased by adding tin in quantities of about 7% besides gold, aluminum and thorium.

Generally, it has proved advantageous to keep the contents of tin in the alloy between 1% and 3%. Good results may also be obtained with lower additions of tin, for instance, 0.1 or 0.2 to 1%. I

An alloy of the following composition Gold Aliuninum 24.25 Thorium 0.25 Tin 0.5

has a beautiful 'blueish color, good workabilit and may easily be hallmarked.

In carrying out my invention I may proceed as follows: The composition AuAlz, i. c. 78.5 parts of gold and 21.5 parts of aluminum, may serve as starting material, whereby one or both of these metals are partly substituted by thorium or thorium and tin.

It has proved advantageous to substitute one part of the aluminum by thorium or thorium and hallmark of 18 karat.

The alloys, according to my invention, may also contain, besides the main constituents gold, aluminum and thorium or thorium and tin, small quantities of other metals such as silver, zinc, cadmium and the like.

Qther components of the alloy may be iron, nickel,.cobalt, manganese, copper. The addition. of small quantities of these metals either alone or a in combination may influence the qualities of the alloys with respect -to ductility and the like and also in regard to the color shade. Of course, the quantity of these additional metals is proportionedin such manner that harmful influences may not occur. Generally, it was found advantageous to.keep the amount of these metallic additions, alone or combined with each other, below 5% preferably below 2% of the total alloy.

As the alloys are susceptible against oxygen, I prefer to work airsealed. For instance, I may proceed in such manner that at first the aluminum is molten under a salt layer whereupon the 78.5% gold, 4.5% to 21.5% aluminum, 0.5% to 10 10% thorium and 0.1% to 7% tin.

3. A workable gold alloy having a purple. colored shade consisting substantially of 68.5% to 78.5% gold, 11.5% to 21.5% aluminum, 0.5% to 7% thorium, and 1% to 3% tin.

4. A workable gold alloy having a purple colored shade consisting substantially of 61.5% to 78.5% gold, 0.25% to 10% thorium, 0.1% to 7% tin and the balance aluminum, the aluminum constituting not over 24.25% of the alloy.

LUDWIG WEISS. 

